Method for monitoring the reversing process of electrically actuatable units

ABSTRACT

The invention relates to a method for monitoring and controlling reversing actions in electrically actuatable units, wherein an actuating drive unit can exert an actuating force in order to move an electrically actuatable unit, and a safety circuit automatically switches off the actuating drive unit after a jamming switch-off time that is predetermined for a movement if no movement occurs despite the triggering of the actuating drive unit. According to the invention, a triggered reversing action results in a temporary extension of the predetermined jamming switch-off time from a short jamming switch-off time t 1  that is predetermined for normal operation to a longer jamming switch-off time t 2  ( 2 ).

TECHNICAL FIELD

Modern motor vehicles are equipped with comfort systems, for examplepower windows or sunroofs. These permit the windows and sunroof to beautomatically opened and closed. The manual operation is controlled forexample with the aid of rocker switches with three switch positions. Oneswitch position activates the opening action, one activates the closingaction, and another switches off the drive motor that generates therespective movement.

PRIOR ART

DE-A 198 09 628 relates to a drive unit for moving a component, forexample a window, a seat, or a sunroof of a motor vehicle. The driveunit has an electric motor with for example three field coil pairs,which is brushless and can therefore be supplied by an electroniccommutation circuit. A safety circuit switches the electric motor offfor example if the moving component begins to pinch a human appendage.The safety circuit reacts to the frequency of signals obtained fromcurrent or voltage fluctuations in at least one electrical transmissionline of the motor.

The subject of DE-A 199 01 855 is a method and device for operating anactuating drive unit in a motor vehicle. The method is comprised amongother things of the fact that an actuating force exerted by theactuating drive unit is measured, this actuating force is compared to alimit force, and the actuating drive unit is reversed if the limit forceis exceeded (closing force limitation).

DE-A 30 34 118 relates to a method for electronically actuating andmonitoring the opening and closing cycle of electrically actuatableunits, for example power windows and electric sunroofs, in particular ofmotor vehicles, as well as an electrical circuit arrangement forexecuting the method. An electrical actuating drive unit connected tothe dc-powered electrical system can be actuated by means of electricalswitches, in particular push buttons. In order to avoid safety defects(the pinching of at-risk appendages such as the neck, head, fingers,etc.), the path traveled is electronically detected during the openingof the unit, this detected opening path is compared to the closing pathtraveled during the closing of the unit, and the speed of the electricactuating drive unit during closing is detected and electronicallycompared to a constant standard value. When there is a reduction inspeed during closing, the actuating drive unit is switched off. This isintended to reduce the safety defects such as the pinching of at-riskappendages during the closing of the electrically actuatable units.

In the prior art, the actuating drive unit is also switched off if oneof the electrically actuatable units jams, in order to thus prevent amechanical or electrical overload of the actuating drive unit. Thisswitching off is triggered after a predetermined jamming switch-off timehas elapsed in which the unit has been jammed in the opening or closingdirection. Usually the jamming switch-off time is predetermined as aperiod of between 100 ms and 500 ms.

This jamming switch-off time, however, can be disadvantageous if areversing of the actuating drive unit is triggered (for example due to apinching emergency), but is not possible because of temporary voltagedips in the operating voltage. If the voltage dips last longer than thejamming switch-off time, then the evaluation electronics switch thedrive unit off in the same way as when there is a jam. A pinchedappendage is therefore no longer released.

Then a reversal from the closing action to the opening action of theactuating drive unit is not possible, for example, if the operatingvoltage (e.g. the electrical system voltage of a motor vehicle)temporarily drops below the relay pick-up voltage of the relay that isused to switch to the opening action. In this connection, the relaypick-up voltage is understood to be the value of the lowest voltage thatcauses a relay to switch. Among other things, this relay pick-up voltagedepends on the additional wiring (for example a protective diode beforethe relay winding), the ambient temperature, the self-heating, and theinternal resistance of the relay driver, and is typically between 8 and10 V. The relay holding voltage required to hold the switched relay inthe switch position, however, is lower than the relay pick-up voltage. Alow operating voltage (electrical system voltage) can therefore be highenough to exceed the relay holding voltage and still be lower than therelay pick-up voltage. In this case, it is possible, for example, tohold the relay—which is for switching to the closing action—in theclosed switch position, but it is not possible to reverse the actuatingdrive unit by switching the relay for the opening action since thevoltage falls below the required relay pick-up voltage. As a result, theunit to be actuated does not move in the opening direction. A possibleresult then, as described above, is that the drive unit is switched offafter the jamming switch-off time has elapsed.

DEPICTION OF THE INVENTION

The embodiment according to the invention has the advantage that itassures the automatic releasing of a pinched appendage even in the eventof a temporary drop in operating voltage. This results in an improvedsafety behavior of electrically actuatable units at a low operatingvoltage. It is also advantageous that no additional sensors are requiredto execute the method according to the invention if position-measuringsensors for the units are already provided. In addition, the methodaccording to the invention is used for indirect relay control with everyreversal switching action of electrically actuatable units, not justwhen a pinching occurs. Electrically actuatable units are understood inparticular to be power windows and sunroofs of motor vehicles and, forexample, also electrically actuatable sliding doors, seats, convertibleroofs, and hoods.

These advantages are attained according to the invention by means of amethod for monitoring and controlling reversing actions in electricallyactuatable units, in which an actuating drive unit can exert anactuating force in order to move an electrically actuatable unit, and asafety circuit automatically switches off the actuating drive unit aftera jamming switch-off time predetermined for a movement has elapsedduring which no movement has occurred despite the fact that theactuating drive unit is switched on. According to the invention, atriggered reversing action temporarily results in an extension of thepredetermined jamming switch-off time from a short jamming switch-offtime t₁ predetermined for normal operation to a longer jammingswitch-off time t₂.

Reversing actions are understood to be actions in which a triggeredaction is reversed. For example, an opening action of a power window ina motor vehicle is interrupted and a closing action is activated orconversely a closing action is interrupted and an opening action isactivated.

In motor vehicle power windows, actuating drive units can, for example,contain one of two different systems: a linkage having only turning andsliding pairs or a linkage with a Bowden cable. In the purely turningand sliding linkage, a drive motor (electric motor) sets a spur gear inmotion in order to drive a toothed segment connected to the turning andsliding linkage. In the Bowden cable linkage, the drive motor drives aBowden cable arrangement. In this connection, an actuating drive unit isunderstood to encompass a drive motor and a linkage.

The safety circuit automatically switches off the actuating drive unitwhen a jamming of the electrically actuatable unit is detected thatlasts longer than a predetermined jamming switch-off time. A jamming isdetected when the actuating drive unit is triggered, but no positionchange of the electrically actuatable unit is detected. For example, ajamming is detected if a control element (e.g. a rocker switch)indicates to the control electronics the desired operating mode, forexample the closing of an electric sunroof in a motor vehicle, and thenno position change of the sunroof in the closing direction is detectedwithin a jamming switch-off time (e.g. 500 ms). The triggering of theactuating drive unit in this connection can occur not only manually bymeans of a control element, but also by means of control electronics,for example in a closing force limitation, in which a reversal of theactuating drive unit is triggered as soon as a threshold value of theclosing force is exceeded.

According to the invention, when a reversing action is triggered, atemporary extension of the predetermined jamming switch-off time from ashort jamming switch-off time t₁ predetermined for normal operation to alonger jamming switch-off time t₂ takes place. The short jammingswitch-off time t₁ is predetermined for normal operation in order toprevent a mechanical or electrical overload of the actuating drive unitin the event of a jam. However, it has the disadvantage that when thereare short voltage drops that prevent a triggering of the actuating driveunit (for example because the voltage falls below a relay pick-upvoltage), a jamming is ascertained and the safety circuit switches offthe actuating drive unit. This is particularly dangerous in reversingactions because they may be triggered due to an emergency (the pinchingof an appendage). In such an emergency, if no movement in the reversedirection occurs within the short jamming switch-off time (because theoperating voltage is temporarily too low), then the actuating drive unitis switched off. There is thus a greater risk of injury for the personwhose appendage has gotten pinched since he is no longer even releasedin a more delayed fashion once the operating voltage returns to asufficient level. The predetermining of a longer jamming switch-off timet₂ during the initiation of a reversing action solves this problem sincenow, a temporary jamming of the actuating drive unit no longer resultsin a final switching-off of the actuating drive unit. Temporary jams forexample due to short drops in the operating voltage, are bridged over bya longer jamming switch-off time t₂.

If the short jamming switch-off time t₁ in power windows of motorvehicles, for example, lies between 100 ms and 500 ms, then a valuebetween 10 s and 50 s, for example, could be predetermined for thelonger jamming switch-off time t₂.

The extension of the jamming switch-off time from t₁ to t₂, however,must only be temporary since otherwise an overloading of the actuatingdrive unit can therefore occur, for example at the actual mechanicalstop of the electrically actuatable unit.

DRAWINGS

The invention will be explained in detail below in conjunction with thedrawings.

FIG. 1 is a flowchart that depicts the course of a method according tothe invention, in which the jamming switch-off time is temporarilyextended with each reversing action,

FIG. 2 is a flowchart that depicts the course of a method according tothe invention, in which the jamming switch-off time is temporarilyextended only when a reversing action is initiated and the operatingvoltage falls below a threshold value, and

FIG. 2 a is a flowchart that depicts the course of another methodaccording to the invention, in which the jamming switch-off time istemporarily extended only when a reversing action is initiated and theoperating voltage falls below a threshold value.

EMBODIMENTS VARIANTS

The flowchart in FIG. 1 represents an embodiment variant of the methodaccording to the invention, in which the jamming switch-off time istemporarily extended with each reversing action.

In the preferred embodiment of the current invention that is shown, thereversing action corresponds to a reversal from a closing action into anopening action.

The aim of activating the reversing action 1 can, for example, be totrigger an opening action in order to release an appendage that has beenpinched during the closing action. The activation of the reversingaction 1 results in an extension of the predetermined jamming switch-offtime 2 from t₁ to t₂. Then the current position 3 of the electricallyactuatable unit is determined and stored, a desired position iscalculated 4, and a jamming counter is set to the predetermined jammingswitch-off time 5.

In a preferred embodiment of the current invention, at least oneposition sensor detects the current position of the electricallyactuatable unit. The position determination 3 can, for example, beexecuted by means of incremental sensors, e.g. by means of Hall sensors.In this connection, it is advantageous to use the position sensors thatare already present so that no additional costs are incurred in order tocarry out the method according to the invention.

In this preferred embodiment of the current invention depicted in FIG.1, the current position of the electrically actuatable unit detected bythe position sensor is stored as a reversing position when the reversingaction 1 is triggered. In the rest of the method according to theinvention, this stored reversing position is used as a comparison valuein order to determine whether a defined position change has occurredsince the activation of the reversing action 1.

The calculation of the desired end position 4 should determine theposition of the electrically actuatable unit that should have beenreached since the actuating drive unit activated the reversing action 1.The desired end position can, for example, be the position of theelectrically actuatable unit in which it is completely open or in whichthe release of a pinched appendage would be reliably assured.

In a preferred embodiment of the current invention, the predeterminedjamming switch-off time is counted down on a jamming counter. In themethod according to the invention depicted in FIG. 1, the jammingcounter is set to the longer jamming switch-off time t₂ after theactivation of the reversing action 1. The jamming counter is decrementedby defined time units during the course of the method according to theinvention. When the jamming counter reaches zero, the predeterminedjamming switch-off time has elapsed.

The next step in the method according to the invention is the activationof the opening action 6. The activation occurs, for example, through theswitching of at least one relay. The actuating drive unit should thus betriggered so that it exerts an actuating force in order to move theelectrically actuatable unit in the opening direction.

Then the at least one position sensor determines the current position 7of the electrically actuatable unit once more. This positiondetermination 7 after the activation of the opening action 6 serves as abasis for the query as to whether a position change has occurred 8. Anaffirmative response to this query 8 (position change has occurred 9) isproduced if the current position (in the opening direction) determinedin the position determination 7 differs from the reversing position thatwas determined and stored in position determination 3. A negativeresponse (position change has not occurred 10) is produced if both ofthe position determinations 3, 7 have yielded the same position.

If the response to query 8 is negative (position change has not occurred10), then the electrically actuatable unit could be jammed. The jammingcounter is therefore decremented 11, i.e. reduced by a defined timeunit. If the response to query 8 is affirmative (position change hasoccurred 9), then the jamming counter is set to the currentlypredetermined jamming switch-off time (23). Then a query is executed asto whether the jamming counter is at zero 12. This would mean that thejamming switch-off time had elapsed. If the response is affirmative(jamming counter has reached zero 13), then the actuating drive unit isswitched off (by a safety circuit) and the opening action 14 is thusterminated. In particular, this serves to protect the actuating driveunit from overloading. If the response to query 12 is negative (jammingcounter has not reach zero 15), then a further query 16 is executed asto whether the electrically actuatable unit has reached the desired endposition calculated in step 4. This query 16 receives an affirmativeresponse (desired end position has been reached 17) if the currentposition determined in step 7 corresponds to the desired end positioncalculated in step 4. Then the electrically actuatable unit has reachedthe desired position and the opening action 14 is terminated (switchingoff of the actuating drive unit). A negative response to the query 16(desired end position has not been reached 18) means that furthermovement of the electrically actuatable unit is required in order toreach the desired end position. As a result, the method according to theinvention continues with a further query 19.

In a preferred embodiment of the current invention, if the positionsensor has detected a movement from the reversal position in thedirection sought by the reversing action within the predeterminedjamming switch-off time t₁ or t₂, then the predetermined jammingswitch-off time is set to the short jamming switch-off time t₁.

In a particularly preferred embodiment of the current invention, thepredetermined jamming switch-off time is set to the short jammingswitch-off time t₁ if the movement in the direction sought by thereversing action that the position sensor detects within thepredetermined jamming switch-off time t₁ or t₂ is equal to or greaterthan a defined desired movement ΔX.

These two embodiment forms of the current invention can be achievedthrough the query 19 and the subsequent action 20 in the methodaccording to the invention depicted in FIG. 1. In query 19, adetermination is made as to whether a certain movement has occurred. Inthe case of the first preferred embodiment of the current inventionexplained above, this would mean that the comparison of the currentposition determined in process step 7 to the reversal positiondetermined in step 3 determines that a movement in the opening directionhas occurred. In the case of the particularly preferred embodiment ofthe current invention explained above, a certain movement is detected ifthe difference between the current position and the reversal positionreaches or exceeds a defined desired movement ΔX.

If the query 19 as to whether a certain movement has occurred receivesan affirmative response 20, then the predetermined jamming switch-offtime is reset to the short jamming switch-off time t₁ 21. If the query19 as to whether a certain movement has occurred receives a negativeresponse 22, then the jamming switch-off time remains unchanged.

After the jamming switch-off time is reset 21 (when the response isaffirmative 20) or left the same (when the response is negative 22), theposition determination in step 7 is repeated. This produces a loop thatis repeated until the last process step 14, the termination of theopening action (switching off of the actuating drive unit).

In the event of an emergency due to the pinching of an appendage, themethod according to the invention depicted in FIG. 1 proceeds asfollows:

The pinching of an appendage during the closing of the electricallyactuatable unit triggers the initiation of a reversing action 1. Thiscan occur, for example, through manual actuation of a control element orautomatically through closing force limitation. As a result, the jammingswitch-off time is extended to t₂ 2, the current position of theelectrically actuatable unit is determined and stored as a reversalposition 3, the desired return position is calculated 4, the jammingcounter is set to the jamming switch-off time t₂ 5, and the openingaction is activated 6. Then the current position of the electricallyactuatable unit is determined again 7, which is required in the query 8as to whether a position change has occurred. If the electricallyactuatable unit has not moved since the activation of the opening action6, for example due to a temporary drop in operating voltage thatprevents a switching of the relay required for the opening action, thenthe jamming counter 11 is decremented. The query 12 as to whether thejamming counter is at zero receives the response “no” after the firstdecrementation so that the method according to the invention continueswith the query 16 as to whether the desired position has been reached.This query 16, like the subsequent query 19, as to whether a certainmovement has occurred will receive a negative response in this instanceso that a position determination 7 is now executed once again.

If query 8 receives an affirmative response 9 in a passage through thisloop, for example because the operating voltage has increased once more,then the jamming counter is set to the currently predetermined jammingswitch-off time 23. If the position change produced has reached thedesired position calculated in step 4, then the opening action isterminated 14 after query 16 and the passage through the loop istherefore interrupted. The pinched appendage is released. If the desiredposition has not yet been reached, then the query 19 is executed. If acertain movement 20 has occurred, for example if the position change isgreater than a defined desired movement that should assure the releaseof a pinched appendage, then the jamming switch-off time is reset backto the shorter one t₁ 21. In step 23, the jamming counter assumes theshort jamming switch-off time. This has the advantage that in the eventof a possibly ensuing actual jamming of the electrically actuatable unitor even of the actuating drive unit, the actuating drive unit is thenswitched off again after the short jamming switch-off time so that nooverload can occur.

In the event of a longer-lasting jamming of the electrically actuatableunit, the method according to the invention depicted in FIG. 1 isinterrupted 14 after multiple passes through the loop after query 12since the jamming counter has then reached zero 13.

FIGS. 2 and 2 a each depict a flowchart of a method according to theinvention, in which the jamming switch-off time is temporarily extendedonly when a reversing action is being initiated and the operatingvoltage falls below a threshold value.

In one embodiment of the current invention, the predetermined jammingswitch-off time is extended from a short jamming switch-off time t₁predetermined for normal operation to a longer jamming switch-off timet₂ if an operating voltage that is required to trigger the reversingaction falls below a predetermined threshold value.

In a preferred embodiment of the current invention, the predeterminedjamming switch-off time is extended from a short jamming switch-off timet₁ predetermined for normal operation to a longer jamming switch-offtime t₂ only if an operating voltage for switching the actuating driveunit with the aid of at least one relay lies in a range close to therelay pick-up voltage of the at least one relay.

In a particularly preferred embodiment of the current invention, thepredetermined jamming switch-off time is extended from a short jammingswitch-off time t₁ that is predetermined in a normal case to a longerjamming switch-off time t₂ only if an operating voltage for switchingthe actuating drive unit with the aid of at least one relay is less thanthe relay pick-up voltage.

FIG. 2 shows the course of a method according to the invention in one ofthese three embodiment forms. After the activation of the reversingaction 1, a query 24 is executed as to whether the operating voltage hasfallen below a defined threshold value. This threshold value can, forexample, be the relay pick-up voltage, which is the minimum voltagerequired to switch the relay for the opening action. But the thresholdvalue can also be greater than the relay pick-up voltage when theoperating voltage is low so that even in the range below the lowoperating voltage, the query 24 receives an affirmative response 25(that the operating voltage lies below the threshold value). Anaffirmative response 25 results in an extension 2 of the jammingswitch-off time to t₂ and a determination and storage 3 of the reversalposition. A negative response 26 (operating voltage is not below thethreshold value) results in the fact that the jamming switch-off time isset to the short jamming switch-off time t₁ 27.

Then the method according to the invention continues with thecalculation of the desired position 4, the setting of the jammingcounter 5, etc. (as described above in conjunction with FIG. 1).

FIG. 2 a shows the course of another method according to the inventionin one of the three embodiment forms mentioned above. After theactivation of the reversing action 1, a query 24 is also executed as towhether the operating voltage has fallen below a defined thresholdvalue. An affirmative response 25 results in an extension 2 of thejamming switch-off time to t₂. A negative response 26 (operating voltageis not below the threshold value) results in the fact that the jammingswitch-off time is set to the short jamming switch-off time t₁ 27. Themethod according to the invention is then continued with the positiondetermination and storage 3, the calculation of the desired position 4,etc. (as described above in conjunction with FIG. 1).

The method according to the invention depicted in FIG. 2 differs fromthe method according to the invention depicted in FIG. 2 a in that theposition determination and storage 3 is not executed in every instance,but only in the event that the query 24 receives an affirmative response25. The query 19 as to whether a certain movement has occurred musttherefore be masked out if query 24 has received a negative response 26and consequently, step 3 has not been executed since a reversal positionstored in step 3 is required in order to make a decision regarding thisquery 19. If the query 19 is masked out, after a negative response 18 tothe query 16, the method according to the invention automaticallycontinues with query 8. In the method according to FIG. 2 a, thedetermination and storage of the reversal position 3 as well as thequery 19 as to the certain movement are executed in every instance. Theposition determination 7 can be executed both as part of the methodaccording to the invention (FIG. 2 a) and in a separate function(modularization principle) (FIG. 2, not shown).

The preferred embodiments of the current invention depicted in FIGS. 2and 2 a represent among other things a universal control as to whetherreversing actions are functioning properly. Even with a sufficientlyhigh operating voltage at which there is no extension of the jammingswitch-off time, the method is executed until one of the two switch-offcriteria 12 (jamming counter at zero) or 16 (desired position reached)has been fulfilled.

In a preferred embodiment of the current invention, the method accordingto the invention is interrupted in the vicinity of mechanical stops ofthe electrically actuatable unit. Power windows in motor vehicles, forexample, strike against a stop when they are completely opened andstrike against another stop when they are completely closed. Shortlybefore one of these two stops is reached, it is advantageous tointerrupt the method according to the invention since the actuatingdrive unit of the window would otherwise run the risk of beingoverloaded due to the extended jamming switch-off time. In this case, aninterruption of the method according to the invention is insignificantwith regard to the danger of pinching. When a motor vehicle window isalmost completely open, there is never any danger of pinching during amovement in the opening direction. In a closing window that is almostcompletely closed, the position at which the method according to theinvention is interrupted should be selected so that the distance to thestop is too small to pinch an appendage.

REFERENCE NUMERAL LIST

-   1 activation of the reversing action-   2 extension of the predetermined jamming switch-off time-   3 position determination and storage-   4 calculation of the desired end position-   5 setting of the jamming counter to the jamming switch-off time-   6 activation of the opening action-   7 position determination-   8 query as to whether a position change has occurred-   9 position change has occurred-   10 position change has not occurred-   11 decrementation of the jamming counter-   12 query as to whether the jamming counter is at zero-   13 jamming counter has reached zero-   14 termination of the opening action-   15 jamming counter has not reached zero-   16 query as to whether the desired end position has been reached-   17 desired end position has been reached-   18 desired end position has not been reached-   19 query as to whether a certain movement has occurred-   20 a certain movement has occurred-   21 resetting of the predetermined jamming switch-off time to the    short-   22 jamming switch-off time-   23 a certain movement has not occurred-   setting of the jamming counter to the current predetermined jamming    switch-off time-   24 query as to whether the operating voltage has fallen below a    threshold value-   25 operating voltage is below the threshold value-   26 operating voltage is not below the threshold value-   27 setting of the jamming switch-off time to the short jamming    switch-off time t₁

1. A method for monitoring and controlling reversing actions inelectrically actuatable units, wherein an actuating drive unit can exertan actuating force in order to move an electrically actuatable unit anda safety circuit automatically switches off the actuating drive unitafter a jamming switch-off time that is predetermined for a movement haselapsed if no movement occurs despite the triggering of the actuatingdrive unit, characterized in that a triggered reversing action resultsin a temporary extension of the predetermined jamming switch-off timefrom a short jamming switch-off time t₁ that is predetermined in anormal case to a longer jamming switch-off time t₂ (2).
 2. The methodaccording to claim 1, characterized in that an extension of thepredetermined jamming switch-off time from a short jamming switch-offtime t₁ that is predetermined in a normal case to a longer jammingswitch-off time t₂ (2) occurs only if an operating voltage required fortriggering the reversing action falls below a predetermined thresholdvalue.
 3. The method according to claim 1, characterized in that anextension of the predetermined jamming switch-off time from a shortjamming switch-off time t₁ that is predetermined in a borderline case toa longer jamming switch-off time t₂ (2) occurs only if an operatingvoltage for switching the actuating drive unit with the aid of at leastone relay lies in a range close to the relay pick-up voltage of the atleast one relay.
 4. The method according to claim 1, characterized inthat an extension of the predetermined jamming switch-off time from ashort jamming switch-off time t₁ that is predetermined for normaloperation to a longer jamming switch-off time t₂ (2) occurs only if anoperating voltage for switching the actuating drive unit with the aid ofat least one relay is less than the relay pick-up voltage.
 5. The methodaccording to claim 1, characterized in that the reversing actioncorresponds to a reversal from a closing action into an opening action.6. The method according to claim 1, characterized in that thepredetermined jamming switch-off time is counted down on a jammingcounter (11).
 7. The method according to claim 1, characterized in thatthe current position of the electrically actuatable unit is detected (7)by at least one position sensor.
 8. The method according to claim 7,characterized in that the current position (3) of the electricallyactuatable unit detected by the position sensor is stored as a reversalposition when a reversing action (1) is triggered.
 9. The methodaccording to claim 8, characterized in that the predetermined jammingswitch-off time is set to the short jamming switch-off time t₁ if withinthe predetermined jamming switch-off time t₁ or t₂, the position sensordetects a movement from the reversal position in the direction sought bythe reversing action.
 10. The method according to claim 8, characterizedin that the predetermined jamming switch-off time is set to the shortjamming switch-off time t₁ if the movement in the direction sought bythe reversing action that the position sensor detects within thepredetermined jamming switch-off time t₁ or t₂ is equal to or greaterthan a defined desired movement ΔX.